The effective (or brake) horsepower (bhp) that an internal combustion engine can deliver is limited to a great extent by the fluid friction losses, or pressure losses, generated both during exhaust of combustion gases from the cylinder (through the exhaust valves) and intake of air to the cylinder (through the intake valves). Such pressure losses increase the mean effective pressure that the piston has to overcome both during the exhaust stroke and the intake stroke, resulting in work being wasted in each cycle and consequently in less useful effective power being delivered by the engine.
Furthermore, the pressure losses during the intake process also reduce the unit air charge (weight or mass of air drawn into the cylinder per intake stroke) and therefore less fuel can be burned effectively in the combustion process. Consequently, this smaller unit air charge also reduces the thermal energy delivered by the combustion process in each cycle and therefore decreases the effective power delivered by the engine For this reason actual engines usually have intake valves of larger size than exhaust valves, since intake pressure losses have greater negative effects than exhaust pressure losses.
Such pressure losses increase almost as the square of engine speed (rpm) and, for a given speed, the pressure losses decrease almost as the square of the valve opening area (flow area). For this reason, it is desirable to increase as much as is possible the valve opening area in order to obtain a greater power output (bhp) from a given engine However, the space available to accomodate the valves is limited and it is not possible to enlarge the valve opening area by either increasing the size or the number of valves per cylinder beyond a certain practical limit for a given size of engine.
Present four-stroke power cycle reciprocating-piston engines have separate valves with separate passages to accomplish the intake of fresh air into the cylinders and to exhaust the combustion gases from the cylinders. Each valve has its own specific duty. The exhaust valves are not used for the intake of fresh air and the intake valves are not used for the exhaust of combustion gases.
The novel idea of the invention Is to make use of all valves of each cylinder (both the intake valves and the exhaust valves) to accomplish both functions: the exhaust of combustion gases and the intake of fresh air. This is done by modifying the program of operation of the valve driving mechanism (the shape or profile of the cams), and by making use of conduits external to the cylinders and provided with a forced air flow produced by an air impeller (either a fan, or a blower, or a compressor) driven by the engine, in order to sweep away the combustion gases towards the exhaust manifold during the exhaust process and to supply sufficient fresh air to the cylinder during the intake process.
The purpose of the above is to greatly increase the valve opening area as well as the period of time of full opening of the valves, for both the intake and the exhaust process. In this manner, the average valve opening area is substantially increased and, since the pressure losses decrease almost as the square of the valve opening area, a very important gain In the power output (bhp) will be obtained, due to less wasted work being accomplished by the pistons and also due to the increase of the unit air charge, as indicated before. Better efficiency Mill also be obtained and the average fuel consumption for a given amount of work will be reduced In
In the engine breathing system of the invention, all valves of each cylinder open gradually from the start of the exhaust process until they reach full opening and remain at full opening for the remainder of the exhaust process. In this way, at the start of the intake process of the next cycle the valves are already fully open Therefore, the time at full opening of the valves is substantially increased for both the exhaust and the intake processes, as compared to the usual engine in which the exhaust valves remain at full opening for a short time, since they have to be closed at the end of the exhaust process. The intake valves follow a similar process since they are closed at the start of the intake process, remain at full opening for a short time and have to be fully closed again at the end on that process
In today's engines, it is usual to design for an early opening of the exhaust valves (approximately 48.degree. before the piston reaches the bottom dead center) with the purpose of increasing the effective opening time of the valves in order to decrease the mean effective pressure during the exhaust stroke and consequently to reduce the work of the piston (negative work for the cycle). This is however,accomplished at the expense of obtaining less work from the combustion gases during the power stroke. The net benefit obtained is positive when the engine operates at high speed and high load, but at low speed and high load (for instance during acceleration) the net effect obtained is negative.
In a similar way, It is usual for the intake valves of present engines to close late (approximately 45.degree. after bottom dead center) with the purpose of increasing the unit air charge obtaining more power from the engine. However, this is accomplished at the expense of decreasing the effective compression stroke and therefore lowering the compression ratio, which in turn decreases the thermal efficiency of the cycle which is a function of the compression ratio. As a consequence, the fuel consumption increases, especially at low speeds and high load (full throttle opening).
Taking into consideration that in the system of the invention the flow area (valve opening area) is much larger, and that the time at full opening of the valves is also longer, it is possible to considerably reduce the early opening of the exhaust valves and/or the late closing of the intake valves, with the purpose of reducing the negative effects mentioned before. It is also possible to maintain the accustomed early opening and late closing of the valves, and make use of the much larger flow area to increase the maximum speed of rotation of the engine, increasing in this way its; maximum power.
It is also possible to make use of said much larger flow area and longer time at full opening of the valves to have a more gradual and consequently smoother opening and closing action of the valves or use it to reduce the stroke of the valves, reducing this way the work spent in driving the valves.
Another advantage of the system of the invention is that a better cooling of the valves and of the engine head is obtained from the fresh air flow through the conduits (or passages) where the valve stems and the external face of the valves are located. Furthermore, due to the dual function of exhaust and intake, all valves will receive a flow of fresh air during the intake process immediately after the exhaust process of hot gases. In present engines, the exhaust valves suffer greatly from overheating since they only handle the hot gases of combustion.
Another advantage of the system of the invention is that it is possible (if desired) to use only one cam to drive all valves of each cylinder since they all have the same functions, opening at the same, time and then closing at the same time. To accomplish this, an element serving as a bridge between the valve stems can be used.
It is worthy of note that although the system of the invention makes use of a fan (or blower or compressor), as some supercharged engines do, it differs from this system. While the purpose of the supercharged is to overcome the fluid friction pressure losses during the intake process, in order to increase the unit air charge, at the expense of work and power which must be delivered by the engine to the supercharger, in the system of the invention such pressure losses are reduced (not overcome) both during the exhaust and the intake processes, obtaining a reduction of the negative work of the pistons and increasing the unit air charge.